Structural highlights of an antioxidative arabinogalactan protein of Lannea grandis gum that stabilizes β-lactoglobulin

Abstract Arabinogalactan proteins (AGPs) are heavily glycosylated proteoglycans in plants. The structural complexity of their glycan portion hampers the assignment of the arabinogalactan protein function and limits their uses. Herein, we report finer structural details of the AGP of Lannea grandis gum based on libraries of oligosaccharides released by Smith degradation, enzyme digestion and partial acid hydrolysis. Application of NMR spectroscopy to the parental AGP, which contained 95% carbohydrate and 3% protein, in combination with chemical, chromatographic and ESI-MS data on oligosaccharides generated allowed direct information on glycosidic linkage type, ring size, anomeric configuration and sequence of saccharide residues. Finally, this AGP shows dose-dependent free radical scavenging activity as well as forms water soluble complex (K = 3.32 × 10 6 /M) with β -lactoglobulin ( β -lg) at pH (2–7).